I don't assert to fully grok what OpenSocial is or isn't (or the business motivations that drove it) but, as near as I can tell, Open Social is about making widgets/gadgets/applications portable across container boundaries. Move the applications around, but the social & profile data stays put thank you very much.
For the life of me, I can't remember a time when 'widget portability' was presented as a problem that needed solving.
Reminds me of the physicist I. Rabi's response to the news of the discovery of the sub-atomic muon particle. On hearing the news, Rabi asked 'Who ordered that?'.